The invention relates to a staff-location and signalling system for use in mines, and more particularly the invention relates to a system comprising one or more base stations distributed over the mine area, the base stations being in voice communication with an exchange and each having a receiving and transmitting device and being adapted for selective coupling, indirectly via secondary wave guides, to radio telephone sets in the mine area in order to produce radio telephone traffic.
In some known systems of the aforementioned kind, used as radio telephone and signalling systems, a radio telephone connection can be made either between an exchange and one or more base stations or between the base stations and radio telephone sets carried by miners in the mine. Compared with omnidirectional systems, systems of the aforementioned kind have the advantage of much greater range, since electromagnetic waves between the parties in communication are transmitted over great distances along secondary wave guides extending through the entire main area. The wave guides may be, for example, transmission lines; metal, water/or compressed-air lines; chains; or rails or the like. The advantage compared with conventional induction radio installations is that there is no need for special wave guides between subscriber stations in the mine area.
However, a voice or signal communication from the exchange or base station can be made only to those miners who carry a radio telephone set. Consequently these are the only people who can be reached by a staff-location or warning signal. For ergonomic and economic reasons, however, it is impossible to equip all mine employees with radio telephone sets.
The object of the invention, therefore, is to provide an improved staff-location and signalling system.